Unit 2

1. Unit 2 Cell Division Mitosis and Meiosis I and II

2. Mitosis Word Meanings • Chromosome • Etymology: Greek : Chromo = colored soma = body • Centromere • Centro= center mere= part • Inter • Etymology: Latin: between • Pro- • Etymology: Greek: before • Meta- • Etymology: Greek: after • Ana- • Etymology: Greek: up • Telo- • Etymology: Greek : end • Cytokenesis • Etymology: Greek: Cyto = cytoplasm kenesis = movement

3. Reasons why a cell needs to divide. • Destroyed cells need to be replaced. • Cell size • Most living cells are between 2 and 200 micrometers in diameter (3 feet = 1 meter = 1 million micrometer) • Limitation of cell size • Surface area to volume ratio • Increase cell size will increase volume of cell • As cells grow, the amount of surface area becomes too small to allow materials to enter & leave the cell quickly enough by diffusion. • Diffusion (see unit 1) • fast & efficient over short distances • If cell gets too large, would decrease diffusion.

4. The nucleus • DNA in the nucleus is copied to make proteins which run the cells activities in the cytoplasm. • Cell size is limited by the amount of proteins the DNA is able to make to control the cell.

5. DNA Packing (occurs before cells divide) DNA is a very long thin molecule (can’t see it) In order to fit in the nucleus it has to get really compact (= packed in closely). The DNA does this by wrapping around proteins called Histones, and folding in on itself This is known as Chromatin.(We can see this) When Chromatin is wrapped up on itself and takes on a distict shape (looks like an “X”) it is known as a Chromosome (We can see this too)

6. Chromosomes • Human cells have 46 Chromosomes • Humans get 23 from the mother and 23 from the father. • Before the DNA wraps up into a chromosome, the DNA gets copied. • Before cell divides each DNA piece winds up into a c’some • One side of the chromosome is the original chromosome • The other side of the chromosome is the copy of the original chromosome. • When a Chromosome is paired we call each side a Chromatid. (You have 2 Chromatids for each Chromosome) • Chromosomes pairs are held together by a centromere. • When the chromatids separate into separate nuclei we call them chromosomes again. Chromatids Centromere

7. After DNA Replication2 pairs per type of chromosome • Individual chromosomes • 1 from each parent Homologous Pairs Dad Mom Before DNA Replication 1 pair per type of chromosome

8. Cell Cycle Interphase – before cell division G1 phase cell growth production of new organelles G0 (G zero) period when cell is not preparing to divide. Here cells lack growth factors Cells stay in the G0 until there is a reason for them to divide. Ex. Muscle, brain, nerve cells S phase = Double the DNA DNA replication (duplicate) Go from 46 to 92 single chromosome molecules per cell in humans G2 phase cell prepares to divide

9. M phase = Mitosis – Cell Division • Prophase • chromosomes shorten, thicken, and become visible • nucleus and other organelles break down and disappear • Organelles called centrioles begin to make spindle fibers

10. Metaphase • spindle fibers become present and attach to centromeres of chromosome pair. • chromosomes line at center of cell (metaphase plate = equator)

11. Anaphase • The Chromatids are pulled apart towards polar ends of the cell.

12. Telophase • New nuclei form around each set of chromosomes • two new cells start to take shape • chromosomes begin to make proteins

13. Cytokinesis • In animal cells • Animal cells undergo cytokinesis by pinching off along their equator • This works because their membrane is flexible.

14. In plant cells • Plant cells cannot do the same as animal cells because of their cell wall. • Plant cells send vesicles filled with cell wall material to their equator where they fuse together. • This fusion creates cell plates that fuse with the cell wall separating the two cells.

15. Cancer • It is the disease where the body’s cells DO NOT STOP mitosis. • Results in tumors forming throughout the body. • A tumor is a bunch of cells in one area of the body that keep dividing. • These cells can then move on to other parts of the body causing tumors to develop in other regions. • Cancer kills by causing your organs to malfunction.

16. Cell Differentiation • Unspecialized cells develop into mature forms and functions • Each cell has a full set of DNA • BUT, each type of cell uses only specific genes on the DNA to carry out its functions • Stem Cells • Can develop into a variety of cell types • Will divide by mitosis into either two stem cells, or, a stem cell and a specialized cell.

18. Mitosis Pop Quiz 1.___________________________ 2._________________________ 4.__________________________ 3.___________________________

19. Meiosis Word Meanings • Homologous • Etymology: Greek homologos : to agree • having the same position, value, or structure • Tetrad • Etymology: Greek • a group or arrangement of four • Dyad • Etymology: Late Latin dyas, from Greek, from dyo • :pair; two individuals • -ploid • having or being a chromosome • Di- • Etymology: Latin, from Greek; akin to Old English twi- • twice :two: double • Ha- • Etymology: Greek :single

20. Somatic cells and Gametes • Somatic cells are body cells. • Make up most of your body cells. • These are diploid (2n) • Have two sets of chromosomes. • 1 set from father & 1 set from mother • Gametes = sex cells(sperm/egg cells) • These are haploid (n) • Have only one set of chromosomes • Types of Chromosomes • Autosomes – contain genes not associated with sex • Sex chromosomes – directly control sexual traits.

21. Meiosis – The creation of sex cells Interphase (G1, S, G2) • All your cells start off as diploid cells = Diploid (2n): cell with two of each kind of chromosome (In humans = 46 [23 from each parent]) • G1 – Cell grows; DNA is long and stringy and is not visible. (so the DNA can be copied) • S – DNA gets replicated (copied). • G2 – Cell continues growing and prepares to divide.

22. Meiosis I Prophase I • The chromatin wind-up, creating chromosomes which can now be seen. • Centriols create Spindle Fibers • Nuclear envelope disappears • Each chromosome pair then actively seeks out its homologous chromosome pair. • Homologous pairs are about the same size and shape • This is called a tetrad (four chromatids) • Crossing Over will now happen. • where two non-sister chromatids exchange genetic material.

23. After DNA Replication2 pairs per type of chromosome Homologous Pairs – each individual chromosome has been copied • Individual chromosomes • 1 from each parent Dad Mom Before DNA Replication 1 pair per type of chromosome

24. Prophase I

25. Metaphase I. • The spindle fibers attach to the centromere on each chromosome pair. • Homologous chromosomes are lined up on the metaphase plate (equator) by the spindle fibers. • 2 rows of 23 chromosome pairs = 46 pairs total

26. Anaphase I • The tetrad gets pulled apart = homologous chromosomes separate. • CHROMATIDS DO NOT GET PULLED APART YET! • Each homologous chromosome moves to opposite poles.

27. Telophase I / Cytokenesis • Individual nuclear envelopes begin to surround the separate chromosome pairs • Cytokenesis separates the one cell in two.

28. END OF MEIOSIS I Two cells are created each with 23 chromosome pairs

29. Meiosis II Prophase II • Each dyad (2 Chromatids = 1 Chromosome pair) are connected by a centromere. • Nuclear envelope disappears • The centrioles create spindle fibers again.

30. Metaphase II • The spindle fibers attach to the centromere on each dyad (1 Chromosome pair = 2 Chromatids). • The dyads are lined up on the metaphase plate (equator) by the spindle fibers. • 1 row of 23 chromosome pairs in each cell.

31. Anaphase II • The individual sister chromatids from each dyad get pulled apart by the spindle fibers • Each sister chromatid ends up on opposite poles of the cell

32. Telophase II / Cytokenesis • The shape of the cell changes, beginning to form two cells. • New nuclei form around each set of chromosomes • The cytoplasm of both cells divides once again. • Four gametes (= sex cells) are now created

33. END OF MEIOSIS II Four unique haploid cells are created, each with a half set of chromosomes compared to the original (Original Parent cell had 46, each daughter cell has only 23 chromosomes). = Haploid (n): cell with only 1 of each kind of chromosome (in humans = 23 chromosomes)

34. Interphase Mitosis Mitosis: Chromosome Number Flow 46 chromosome pairs 46 individual chromosomes 2n 46 individual chromosomes 2n 46 individual chromosomes 2n

35. Meiosis I Interphase 46 individual chromosomes 2n Meiosis I & II Chromosome Number Flow 46 chromosome pairs 23 chromosome pairs 23 chromosome pairs Meiosis II 23 individual chromosomes n 23 individual chromosomes n 23 individual chromosomes n 23 individual chromosomes n